Rhesus monkey rhadinovirus (RRV), a gammaherpesvirus, is a close viral relative of Kaposi's sarcoma (KS)- associated herpesvirus (KSHV or HHV8), the causative agent of three human malignancies, Kaposi's Sarcoma (KS), primary effusion lymphoma, and multicentric Castleman's disease. RRV is an effective model to study the structure and assembly of gammaherpesviruses since it is able to produce high levels of progeny viruses in culture. The insights gained from studying mechanisms governing virally induced cancers can extend to a wide variety of malignancies, helping in the development of new treatments and therapies. Previous data from our laboratory have shown that RRV contains five gammaherpesvirus specific proteins in its tegument (middle) layer and of those, three have unknown functions, including the protein encoded by open reading frame 52, pORF52. Our hypothesis is that pORF52 plays a critical role in the structure of virions (viral particles) and their assembly as well as a potential role in cellular egress via a direct or indirect interaction with critical infrastructural components of the cell known as microtubules (MTs). Our methods of investigation include utilization of a wild-type (WT) RRV and an ORF52 deleted ( 52) RRV bacterial artificial chromosomes (BAC), each of which contains the remainder of the viral genome. Introducing these BACs into cells capable of supporting viral production will allow us to monitor the viral life cycle in the presence or absence of pORF52 production. The first goal will be to determine whether pORF52 is necessary for RRV DNA replication, a step preceding and required for progeny viral production. Quantitative analysis of the levels of individual viral proteins within the BAC containing cells will then help determine the requirement of pORF52 in the production of the various building block proteins necessary for viral assembly. In addition to these analyses, various imaging techniques will generate complementary data, helping us to examine the structure of the individual particles, the gross level of their production within the cells, as well as their intracellular localization and stage of maturation. In addition, media from cells containing either WT or 52 BAC will be assessed for a) infectious virus and b) production of structural viral proteins. Our preliminary results indicate that pORF52 is necessary for production of virus. To test this, 52 BAC containing cells will be complemented with the introduction of exogenous pORF52 and subsequently examined for the presence of infectious virions as described above. Additionally, RRV pORF52 expression by itself leads to its co-localization with, and stabilization of microtubules. Included in the second half of this proposal is a series of experiments that will investigate this potential interaction using microtubule binding assays, immunofluorescence and confocal microscopy, and assays that directly assess physical interactions between these two components. Combined with a series of mutations strategically introduced into pORF52, these approaches will allow the identification of the regions within the protein essential for not only its MT interactions but also its role in the viral life cycle. PUBLIC HEALTH RELEVANCE: The insights gained from studying mechanisms governing virally induced cancers can extend to a wide variety of malignancies, helping in the development of new treatments and therapies. In this application, we propose to characterize the actions of one specific protein in the life cycle of a subfamily of tumor forming viruses called gammaherpesviruses. We hypothesize that this particular protein may play an essential role in the formation of new viral particles and, thus, would be an attractive candidate for targeted anti-viral therapy.